Membrane-bound ribosomes from Bacillus stearothermophilus contain an extra protein which is not found in free ribosomes. In vitro binding assays consisting of purified M-protein, inverted vesicles and ribosomes will be employed to determine if the M-protein is an essential requirement for the attachment of ribosomes to the membrane. The possibility that the M-protein plays a role in the vectorial transport of puromycin-released polypeptide chains across the membrane will also be investigated. Finally, lactoperoxidase-catalyzed iodination will be used as a surface probe to detect both the ribosomal and membrane proteins located at the ribosome-membrane interface. BIBLIOGRAPHIC REFERENCE: Mojica-a, T., Cheung, D. and Friedman, S.M. Effect of transformation to thermophily on ribosome structure and function. Bacteriol. Proc., p. 170 (1977).